Device for tensioning abrasive belts or the like



Dec. 16., 1969 SCHMZLER ETAL 3,483,661

DEVICE FOR TENSIONING ABRASIVE BELTS OR THE LIKE 2 Sheets-Sheet 1 Filed April 26, 1967 INVENTORS I KARL ALBEEt'l/T sawwzzee HANS KJHL ATTORNEY Dec. 16., 1969 K. A. SCHNIZLER ETA!- 3,483,551

DEVICE FOR TENSIONING ABRASIVE BELTS OR THE LIKE Filed April 26, 1967 2 Sheets-Sheet 2 KARL 4452:5017 scmv/zu e HAM: KJHI.

M ATTORNEY INVENTORS Uited States Patent O rm. Cl. B24b 21/60, 23/06, 25/00 US. Cl. 51148 17 Claims ABSTRACT OF THE DISCLOSURE The abrasive belt of a belt grinder or polisher is tensioned from within by a tensioning roll which is mounted on the longer arm of a pivotable lever whose shorter arm makes on obtuse angle with the longer arm. The lever is rockable on a support which can be afiixed to the main frame of a belt grinder or polisher, and the shorter arm of the lever is biased by a helical contraction spring operating between the lever and the support. The axis of the spring makes with the shorter arm an acute angle so that the product of the effective length of the shorter arm and the momentary bias of the spring remains unchanged in several angular positions of the lever. This enables the wheel to bias the belt with a practically constant force.

CROSS-REFERENCE TO RELATED APPLICATION A belt grinder or polisher which can utilize the tensioning device of the present invention is disclosed in our copending application Ser. No. 633,932, filed Apr. 26, 196-7 and entitled Grinding or Polishing Machine.

BACKGROUND OF THE INVENTION The present invention relates to tensioning devices for abrasive belts or the like. More particularly, the invention relates to improvements in tensioning devices which can be utilized in so-called belt grinders or polishers wherein an oscillatable pressure roll engages the abrasive belt from within and rides over the surfaces of successive workpieces which are conveyed past the belt.

In presently known belt grinding or polishing machines, the tensioning wheel is mounted on a holder which compn'ses two telescopically connected sections. That section which carries the tensionin g wheel is biased away from the other section and the tensioning wheel engages the belt from within to take up the slack when the pressure roll rides over a series of uneven surfaces or over surfaces which are located at different levels. A serious drawback of such tensioning devices is that, in order to avoid undesirable wobbling, the sections of the holder must be fitted into each other with considerable precision which causes excessive friction and wear when the tensioning wheel reciprocates in response to oscillation of the pressure roll. Such friction delays movements of the tensioning wheel in response to oscillation of the pressure roll so that the finish of surfaces on successive workpieces is often very unsatisfactory, particularly if the belt must treat surfaces which are located at different levels. Furthermore, a relatively narrow abrasive belt has a tendency to increase its length and, if the tensioning wheel cannot compensate for P force also contributes to friction between the telescoped sections of the holder and prevents immediate reaction of the tensioning wheel to oscillations of the pressure roll. Finally, presently known tensioning devices cannot be used in connection with belts of various widths unless they are furnished with a large number of spare springs and with complicated accessories for facilitating mounting and detachment of springs.

It is an important object of our invention to provide a novel and improved tensioning device for abrasive belts or the like which is constructed and assembled in such a way that it can be readily mounted in presently known belt grinders or polishers, that it can subject an abrasive belt to practically constant bias despite the fact that the belt might be used in grinding, polishing, bufiing or analogous treatment of uneven surfaces or in treatment of a succession of surfaces which are located at different levels, and that the tensioning device can be readily adjusted to apply necessary bias to longer, shorter, wider or narrower belts.

Another object of our invention is to provide a tensioning device of the just outlined character wherein a single spring often suffices for satisfactory engagement between the tensioning wheel and a wide, narrow, long or short belt.

A further object of the invention is to provide the tensioning device with novel means for changing the bias of its spring.

An additional object of the invention is to provide a novel support for the tensioning wheel in a device of the above outlined characteristics.

A concomitant object of the invention is to provide a tensioning device wherein the bias of the spring which urges the tensioning wheel against an endless abrasive or like belt can be changed by exertion of a relatively small force, wherein the means which is used to change the bias of the spring can remain permanently installed on the tensioning device, and wherein such bias changing or selecting means may also serve to move the tensioning wheel to a position in which the operators can readily remove or apply an endless abrasive belt.

An ancillary object of the invention is to provide a tensioning device wherein the position of the tensioning wheel can be readily and rapidly adjusted so as to properly engage a relatively narrow or relatively wide belt, and wherein the tensioning wheel can be readily removed and replaced by a larger, smaller, wider or narrower tensioning wheel.

Another object of the invention is to provide a tensioning device which is particularly suited for use in so-called belt grinders or belt polishers wherein a pressure roll oscillates to maintain successive increments of a travelling abrasive belt in continuous contact with surfaces on a series of travelling workpieces.

An additional object of the invention is to provide a tensioning device of the just outlined character wherein the tensioning wheel can maintain the belt under substantially constant tension despite the fact that the pressure roll might be required to oscillate at a very high amplitude and/or frequency and wherein the tensioning wheel can respond without undue delay to any, even minor, changes in the position of the pressure roll.

SUMMARY OF THE INVENTION One feature of our invention resides in the provision of a device for tensioning abrasive belts or the like, particularly for tensioning of belts in grinding or polishing machines of the type wherein the belt is trained around pulleys and is engaged from within by a pressure roll which is oscillatable while it tracks an uneven surface or a series of surfaces located at different levels. The tensioning device comprises a support which can form part of or is detachably secured to the main support or frame of a belt grinder or polisher, a carrier lever mounted on the support for pivotal movement about a fixed axis and hav ing a longer arm and a shorter arm making an obtuse angle with the longer arm, a tensioning roll or wheel mounted on the longer arm for rotation about a second axis which is parallel to the pivot axis of the lever and being movable with the lever between a plurality of positions, and biasing means including a helical contraction spring operating between the shorter arm of the lever and the support in such a way that its axis makes an acute angle with the shorter arm. The product of the effective length of the shorter arm and the momentary bias of the spring is substantially constant, and the longer arm is substantially normal to the direction of pull of the belt upon the tensioning wheel. This insures that the bias of the tensioning wheel upon the belt remains practically constant despite the fact that the tensioning wheel might oscillate about the pivot axis of the lever when the aforementioned pressure roll rides over an uneven surface or over a series of surfaces located at different levels.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved tensioning device itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of a specific embodiment with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an end elevational view of a tensioning device which embodies one form of our invention;

FIG. 2 is a side elevational view of the tensioning device as seen in the direction of arrow II in FIG. 1 with the tensioning wheel shown in idle position;

FIG. 3 is a similar side elevational view but showing the tensioning wheel in operative position; and

FIG. 4 is a diagrammatic side elevational view of a belt grinder or polisher which embodies the tensioning device of FIGS. 1 to 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 4, there is shown a belt grinder or polisher which can embody the tensioning device of our invention. This belt grinder or polisher comprises a frame or main support 50 for two pulleys 51, 52 one of which is driven by an electric motor or the like, a lever 53 which is pivotable about the axis of the pulley 51 and carries a pressure roll 54, a second support including an elongated holder 1 which is detachably affixed to the main support 50 and carries at its upper end a tensioning wheel 9, and an endless abrasive belt 31 which is trained around the roll 54, wheel 9 and pulleys 51, 52. The pressure roll 54 is biased against the lower stringer of the belt 31 from within in a manner as disclosed in our aformentioned copending application so that it can ride over an uneven surface or over a succession of surfaces located at difierent levels. Such surfaces are provided on workpieces 55 which are advanced by a suitable conveyor 56 at a level below the lower stringer of the belt 31.

Our present invention is concerned with the device which tensions the belt 31 with a substantially constant force despite the fact that the pressure roll 54 might oscillate about the axis of the pulley 51 when the lower stringer of the belt 31 treats a succession of workpieces 55 whose top surfaces are disposed at different levels. This tensioning device includes the aforementioned second support and the tensioning wheel 9 and is shown in full detail in FIGS. 1, 2 and 3.

The second support (i.e., the support Whichforms part of the tensioning device) further comprises a bearing member orbracket 2 which is turnably and axially movably mounted on the holder 1 and can be fixed in 7 selected angular and axial positions by means of bolts.

screws or analogous fasteners 3. That portion of the bracket 2 which surrounds the holder 1 is slotted so that the bracket can be shifted or turned in response to loosening of the fasteners 3. The position of the bracket 2 with reference to the holder 1 will be changed when the belt 31 is replaced by a considerably longer or shorter belt. The upwardly bent portion of the bracket 2 carries a shaft 5 for a two-armed carried lever 4. The longer arm 6 or' the carrier lever 4 is bifurcated and carries an axially adjustable pivot member 7 for the tensioning wheel 9. This tensioning wheel is mounted on a dustproof antifriction ball bearing 9a on the pivot member 7 and the latter can be fixed in selected axial position by screws 8. The axial adjustability of the pivot member 7 enables the operator to place the tensioning wheel 9 in accurate registry with the pressure roll 54. The shorter arm 10 of the carrier lever 4 holds an eye 11 for one end of a biasing means here shown as being constituted by a strong helical contraction spring 12. The spring 12 operates between the'carrier lever 4 and the holder 1 in such a way that the lever 4 is permanently biased in a counterclockwise direction, as viewed in FIGS. 2 or 3, and with an unchanging force irrespective of the angular position of the carrier lever. This is due to the fact that the arms 6, 10 of the carrier lever 4 make an obtuse angle 34 and that the axis 35 of the spring 12 makes an acute angle 36 with the axis of the shorter arm 10. The angle 34 is located at that side of the carrier lever 4 which faces away from the pressure roll 54. V

The other or lower end of the spring 12 is connected with a second eye 13 provided on a sleeve-like retainer 14 which is slidable on the holder 1 at a level below the bracket 2. This retainer 14 forms part of the means for adjusting the bias of the spring 12 and can be temporarily fixed to the holder 1 in selected axial position by a detent assembly including a spring biased pin or stud 15 providing on the retainer 14 and a'series of longitudinally spaced recesses or bores 16 provided in the peripheral surface of the holder 1.

The adjusting means for changing the bias of the spring 12 further comprises a notched bar or rack 17 which is pivotally secured to the retainer 14, as at 17a. and is biased by a weak helical spring 17b which tends to maintain it in abutment with the holder 1. The rack 17 has a series of longitudinally spaced notches 18 each of which can receive a motion transmitting roll or stud 20 provided on one arm of an actuating member or handle 19 pivotably mounted on the holder at 19a and having at the free end of another of its arms a knob 21. The handle 19 is further provided with a stop 38 which can abut against the holder 1 when the knob 21 is moved to the lower end position shown in FIG. 2, such lower end position corresponding to the idle or lowermost position of the tensioning wheel 9. A suitable locking device 22 is provided to fix the handle 19 in se lected angular position.

The handle 19 comprises a plate-like third arm 23 which supports a pivot pin 24 for the lower end of a pivoting or rocking rod 25 the threaded upper end 27 of which is longitudinally movably and adjustably connected to the longer arm 6 of the carrier lever 4 by a coupling means including a pin 26 mounted on the arm 6 and having a diametral slot for the upper end 27 of the rod 25, and one or more nuts 28 which mesh with the upper end 27 at a level above the pin 26. The arrangement is such that the nuts 28 rock the carrier lever 4 in 'a clockwise direction, as viewed in FIG. 3, when the handle 19 is pivoted toward the position of FIG. 2, but

a coupling element 29 which can be connected with a complementary coupling element on the aforementioned main support 50 (FIG. 4) and can be afiixed to the complementary coupling element by a manually turnable locking bolt 30. The holder 1 will be detached from the main support 50 when the machine of FIG.. 4 is to be used as a wheel grinder, buffer or polisher. The pressure roll 54 is then replaced by a suitable buffing, polishing or grinding wheel and the belt 31 is removed. The manner in which the belt grinder or polisher of FIG. 4 can be converted into a wheel grinder, polisher or buffer is fully disclosed in our aforementioned coperrding application.

The coupling element 29 is preferably turnable with reference to the main support 50 but can be non-rotatably afl'ixed thereto.

Referring again to FIG. 3, the arrow 32 indicates the direction of pull exerted by the belt 31 upon the tensioning wheel 9. When the wheel 9 is operative to bias the belt 31, the longer arm 6 of the carrier lever 4 is substantially normal to the direction indicated by the arrow 32. Therefore, the effective length 33 of the longer arm 6 varies very little or not at all when the carrier lever 4 pivots with reference to the bracket 2 The actual bias of the sp ing 12 upon the tensioning ;wheel 9 remains practically unchanged in each angular position of the carrier lever 4. This is due to the fact that the effective length 37 of the shorter arm 10 decreases when the spring 12 is extended so that its bias increases, and that the effective length 37 of the arm 10 increases when the spring 12 is free to contract and to reduce its bias. Thus, the product of the length 37 and momentary bias of the spring 12 remains practically constant, i.e., the torque transmitted by the spring 12 to the carrier lever 4 remains unchanged in each angular position of the carrier lever. Since the effective length 33 of the longer arm 6 is also nearly constant (in the expected range of positions of the carrier lever), the wheel 9 maintains the belt 31 under unvarying tension despite the fact that the pressure roll 54 rides over an uneven surface or that the pressure roll 54 rides over a succession of surfaces which are located at difierent levels as shown in FIG. 4.

FIGS. 1 and 2 illustrate the tensioning device in idle position in which the belt 31 can be removed to be replaced by a fresh belt or by a wider or narrower belt. In order to move the tensioning wheel 9 to the idle position of FIG. 2, the operator disengages the locking device 22 and pivots the handle 19 in a clockwise direction from the end position of FIG. 3 to the end position of FIG. 2. This pivotal movement is terminated when the stop 38 of the handle 19 abuts against the holder 1. During the first stage of such pivotal movement of the handle 19, the nuts 28 on the upper end 27 of the pivoting or rocking rod 25 travel downwardly toward the pin 26 of the longer arm 6 without causing any angular displacement of the carrier lever 4. During the last stage of such pivotal movement, the nuts 28 pivot the carrier lever 4 in a clockwise direction, as viewed in FIG. 3, and the pivot pin 24 at the lower end of the rod 25 moves toward, through and past a dead-center position until the stop 38 reaches the holder 1. In the dead-center position of the pivot pin 24, its axis is coplanar with the axes of the pivot 19a for the handle 19 and the pivot pin 26. The stop 38 is then biased against the holder 1 by the spring 12 which acts upon the rod 25 through the intermediary of the carrier lever 4, pin 26 and nuts 28. In other words, the handle 19 is automatically located in the end position of FIG. 2 until the operator decides to move the knob 21 upwardly.

If the person in charge wishes to change the bias of the spring 12, the stud 15 of the detent assembly is temporarily withdrawn from the registering recess 16 and the handle 19 is pivoted from the position of FIG. 3 to the approximate level of a selected notch 18 in the rack 17. The latter is then pivoted about the pin 17a so that the roll or stud of the handle 19 can enter the selected notch. In the last step, the handle 19 is pivoted in a counterclockwise direction to move the rack 17 downwardly until the stud 15 on the retainer 14 registers with another recess 16 of the holder 1. The stud 15 is then pushed into the adjoining recess 16 and the roll 20 can be disengaged from the rack 17 so that the latter is free to follow the bias of its spring 17b and to return into a position of parallelism with the holder 1.

In the position of FIG. 3, the tensioning wheel 9 is held in operative position in which it biases the belt 31 with a desired force. The knob 21 of the handle 19 has been moved to its upper end position and the handle 19 may but need not be fixed in such position by the locking device 22. The nuts 28 are located above and are spaced from the pin 26 so that the tensioning wheel 9 can move up and down without any interference on the part of the rod 25. As a matter of fact, the handle 19 will automatically pivot toward the position of FIG. 3 as soon as it is displaced sufiiciently to move the pivot 24 for the lower end of the rod 25 beyond the aforementioned dead-center position. This will be readily understood since the spring 12 then biases the handle 19 in a counterclockwise direction. The length of the rod 25 is such that the nuts 28 can be moved to a plurality of axial positions. The exact position of the lower nut 28 Will determine the position of the tensioning roll 9 in the idle position of FIG. 2. The bottom surface 39 of the lower nut 28 is invariably spaced from the pin 26 when the tensioning wheel 9 is in actual use to insure that the tensioning wheel can oscillate without any interference on the part of the handle 19, rod 25 and nuts 28.

The more important advantages of our tensioning device can be summarized as follows:

The bias of the tensioning wheel 9 upon the belt 31 remains practically unchanged even if the pressure roll 54 must oscillate at a very high amplitude and/or frequency. Also, the tensioning wheel 9 reacts without any delay because the holder 1 need not be assembled of telescopically connected sections. Friction which develops when the carrier lever 4 pivots with reference to the bracket 2 is negligible and has no appreciable effect upon the bias of the tensioning wheel 9. This insures that the finish of surfaces on the workpieces 55 will be much more satisfactory than by resorting to presently known belt grinders or polishers because the tensioning wheel 9 will react, practically instantaneously, to any, even minor, changes in angular position of the lever 53 for the pressure roll 54. Manipulation of the means for changing the bias of the spring 12 can be entrusted to semiskilled persons and the bias of this spring can be changed by exertion of a small effort. The tensioning device can be attached to a belt grinder or polisher in any desired position, i.e., irrespective of whether the pressure roll 54 biases the belt 31 upwardly, downwardly or sideways. Moreover, and since the tensioning wheel 9 is readily detachable with the pivot member 7, it can be replaced by a wider, narrower, smaller or larger tensioning wheel. The wheel 9 can be used with narrower or wider belts because it can be shifted with the pivot member 7 to move nearer to or further away from the longer arm 6 of the carrier lever 4.

Of course, it is equally within the purview of our invention to omit the means for changing the bias of the spring 12 and to furnish the tensioning device with two or more springs each of which has a different characteristic.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art ai'id, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

1. A device for tensioning abrasive belts or the like, particularly for tensioning belts in grinding or polishing machines wherein the belt is trained about pulleys and is engaged from within by an oscillating pressure roll, comprising a support; a carrier in form of a lever mounted intermediate its ends on said support for pivotal movement about a fixed axis, said lever having a first and a second arm including an obtuse angle with each other; a tensioning wheel supported on said first arm for rotation about a second axis and movable with said carrier between a plurality of positions, said tensioning wheel engaging the belt from within and said first arm being substantially normal to the pull of the belt; and spring means connected at opposite ends to said second arm and said support and arranged to operate in a direction which makes an acute angle with said second arm to permanently urge said carrier in one direction with a force which is substantially constant in each position of said carrier.

2. A device for tensioning abrasive belts or the like, particularly for tensioning belts in grinding or polishing machines wherein the belt is trained around pulleys and is engaged from within by an oscillatable pressure roll, comprising a support including an elongated holder and a bearing member turnably and longitudinally movably secured to said holder; a carrier mounted on said holder for pivotal movement about a fixed axis; a tensioning wheel mounted on said carrier for rotation about a second axis and movable with said carrier between a plurality of positions; and biassing means operating between said carrier and said support to permanently urge said carrier in one direction with a force which is at least nearly constant in each position of said carrier.

3. A device for tensioning abrasive belts or the like, particularly for tensioning belts in grinding or polishing machines wherein the belt is trained around pulleys and is engaged from within by an oscillatable pressure roll, comprising a support including an elongated holder; a carrier mounted on said support for pivotal movement about a fixed axis; a tensioning wheel mounted on said carrier for rotation about a second axis and movable with said carrier between a plurality of positions; helical spring means cooperating with said carrier to permanently urge the latter in one direction with a force which is substantially constant in each position of said carrier; and means for adjusting the bias of said spring means and comprising a retainer reciprocably mounted on said holder, one end of said spring means being connected to said carrier and the other to said retainer.

4. A device as defined in claim 3, wherein said retainer comprises a sleeve which is slidable on said holder.

5. A device as defined in claim 3, further comprising detent means for releasably securing said retainer to said holder in one of a plurality of positions each of which corresponds to a diflerent bias of said spring.

6. A device as defined in claim 5, wherein said detent means comprises a plurality of longitudinally spaced recesses provided in said holder and a detent member carried by said retainer and insertable into a selected recess of said holder.

7. A device as defined in claim 3, wherein said bias adjusting means further comprises means for moving said retainer longitudinally of said holder.

8. A device as defined in claim 7, wherein the means for moving said retainer comprises a rack pivotally secured to said retainer and having a plurality of notches, and an actuating member pivotably secured to said holder and having a motion transmitting member receivable in a selected notch to move said rack and said retainer lengthwise of said holder in response to pivotal movement of said actuating member.

9. A device as defined in claim 8, wherein said actuating member comprises a handle having a plurality of arms.

10. A device as defined in claim 7, wherein the means for moving said retainer comprises an actuating member pivotally secured to said holder and further comprising rocking means for pivoting said carrier in response to pivoting of said actuating member.

11. A device as defined in claim 10, wherein said rocking means comprises a rod having a first end articulately connected with said actuating member and .a second end. and coupling means adjustably connecting said second end with said carrier.

12. A device as defined in claim 11, wherein said actuating member comprises stop means arranged to abut against said holder in an end position of said carrier.

13. A device as defined in claim 11, wherein said actuating member comprises an arm provided with pivot means for the first end of said rod.

14. A device as defined in claim 11, further comprising locking means for releasably fixing said actuating member in selected angular positions.

15. A device as defined in claim 11, wherein said coupling means comprises a pin secured to said carrier and having a bore slidably receiving the second end of said rod, and at least one nut provided on said second end to prevent withdrawal of the rod from said pin.

16. A device as defined in claim 1, further comprising dustproof antifriction bearing means provided on said carrier for said tensioning Wheel.

17. A device as defined in claim 1, further comprising a pivot member axially movably mounted on said carrier and fastener means for securing said pivot member in selected axial positions, said Wheel being mounted on said pivot member.

References Cited UNITED STATES PATENTS 1,735,903 11/1929 Johnson 51-141 1,927,330 9/1933 Williams 51l38 3,095,674 7/1963 Lee 51141 OTHELL M. SIMPSON, Primary Examiner 

